Officials say the two tundra swans found dead in the Mendenhall Wetlands State Game Refuge in Juneau on New Year’s Eve died from emaciation.

Alaska Wildlife Troopers sent one of the swans to be examined at the National Wildlife Health Center in Madison, Wisc., and troopers received a report from the organization on Tuesday.

They ruled the cause of death as “emaciation of unknown cause,” said trooper Aaron Frenzel. Emaciation is substantial weight loss and can be caused by starvation.

Troopers initially suspected the birds may have been shot, but Frenzel says the report does not indicate they were poached. Poison was also ruled out as the cause of death.

Troopers were alerted to the case when a man walking the refuge found the swans and reported his find to authorities.

The Alaska Department of Fish and Game estimates there are about 100 tundra swans that visit Juneau each year on their migratory path. They are attracted to the tidal salt marshes in the 3,500-acre refuge and feed on aquatic vegetation there, according to Ryan Scott, area management biologist for the Alaska Department of Fish and Game.

Most of the tundra swans migrating through Juneau likely breed in the Bristol Bay lowlands, although some birds from the Yukon-Kuskokwim Delta pass through, said Craig Ely, a research wildlife biologist with the U.S. Geological Survey’s Alaska Science Center.

Ely said in a phone interview that the birds begin migrating south in September or early October, and return north in a few months later. If they were still in Juneau in January, “that’s really suspect,” Ely said.

It could mean they missed the migration south or were too early returning to Alaska.

Ely said if the pair of swans were young, it’s possible they might have been hatched late and not strong enough to make the trek, or they could have been injured and unable to care for themselves.